Influence factors on the critical micelle concentration determination using pyrene as a probe and a simple method of preparing samples

The critical micelle concentration (CMC) is an important parameter of widely used surfactants and needs to be measured in the application and development of surfactants. Fluorometric method is a widely used method determining CMC values owing to the advantages of highly sensitivity, fast response and wide application range. There are two common methods (I and II) of preparing samples for CMC fluorometric determination. In the process of developing CMC probes with aggregation-induced emission (AIE) characteristics, we found that methods I and II were not suitable for CMC probes with AIE charateristics and developed a new sample preparation method (III), which is not only suitable for CMC probes with AIE characteristic but also decreases operation procedures and errors owing to omitting the addition of micro amount of dyes into each sample. To ascertain if method III is also suitable for other CMC probes without AIE characteristics, the CMC values of surfactants were determined by fluorometric method using widely used pyrene without AIE charateristic as probe and methods I–III to prepare samples. The obtained experimental results proved that method III not only was suitable for preparation of samples for CMC determination of surfactants using pyrene as probe but also led to the least average deviation (methods I–III led to ±0.13, ±0.34 and ±0.05 mM deviation for the CMC determination of sodium dodecyl sulfate (SDS), respectively). The CMC determination using pyrene as probe is based on its change in the ratio (IFIII/IFI) of its emission peaks I and III with surfactant concentration. Unexpectedly, it was found that the IFIII/IFI value of pyrene in surfactant solutions is sensitive to the measurement conditions changing exciting light energy, such as slit widths and sample-measured number. In addition, it was found that surfactant SDS or cetrimonium bromide from different suppliers not only has significantly different CMC values but also leads to very different IFIII/IFI values of pyrene in a certain concentration of surfactant, which can be used as a simple method to distinguish the same surfactant with different CMC values.


Decision letter (RSOS-192092.R0)
13-Jan-2020 Dear Professor Zhu: Title: Influent factors on pyrene-based CMC determination and a simple method of preparing samples Manuscript ID: RSOS-192092 Thank you for your submission to Royal Society Open Science. The chemistry content of Royal Society Open Science is published in collaboration with the Royal Society of Chemistry.
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RSC Subject Editor:
Comments to the Author: (There are no comments.) ********************************************** Reviewers' Comments to Author: Reviewer: 1 Comments to the Author(s) This work concerning the new method for measuring CMC value. This manuscript previously was submitted to RSC Advances, and I was one of the referees. The former version of this manuscript was rejected by me, because of the applicability of analytical method. The authors mentioned something like "which demanded the same fluorospectrometer, the same excitation and emission slit widths of the same fluorospectrometer and even the same measured number for sample measurement." I believed that this type of new method for measuring CMC value is useless.
For this revised manuscript submitted to Royal Society Open Science, the paragraph like "which demanded the same fluorospectrometer, the same excitation and emission slit widths of the same fluorospectrometer and even the same measured number for sample measurement." has been deleted by the authors. However, nearly all the data included in the revised manuscript are same as that of in previous paper. Therefore, the authors should demonstrate the reliability of their methods with a point by point response to the reviewer's comments, before this paper can be published.
My reports for the former version of this manuscript was copied below: In this manuscript, depending on their previously invented sample-preparation method (III), the authors are trying to develop a new method for measuring CMC value by using pyrene as probe.
Although quite a lot of data were included, this work still cannot be published in present state. The reasons are as following: 1, A useful analytical method should have better applicability. Obviously, the things like "which demanded the same fluorospectrometer, the same excitation and emission slit widths of the same fluorospectrometer and even the same measured number for sample measurement." are completely useless. 2, The authors should explain why the surfactant SDS or CTAB from different suppliers have different CMC values. Is there any impurity? 3. The editing of the paper is very careless. For example, "The main text of the article should appear here with headings as appropriate." appears at the beginning of main text. And there is "Bibliography" before each reference.

Reviewer: 2
Comments to the Author(s) Critical micelle concentration (CMC) is an important parameter of surfactants with wide applications. The determination of CMC using fluorescence dyes should be a general method. In this work, the authors compared the conventional methods (I and II) and the method (III) developed for CMC probes with aggregation-induced emission (AIE) characteristics. This work is well conducted and organized. This topic is interest and should be of broad audience. I recommend the acceptance after the following issues could be addressed. 1. The determination of CMC of surfactants using fluorescence has been extensively inverstigated previously. Why the authors choose to use the AIEgens to determine the CMC. 2. The advantages using AIEgens to determine the CMC of surfactants should be clearly described during revisions. 3. The AIE effect has also be utilized for determination of the CMC of AIEgens-containing amphiphilic copolymers. I suggest the authors add some contexts about the AIEgens-containing copolymers and their applications. Some related reviews and reports (e.g., Chemical reviews 109  Thank you very much for further considering our revised manuscript version entitled "Influent factors on pyrene-based CMC determination and a simple method of preparing samples" for publication in Royal Society Open Science.
We also thank the reviewers for their constructive comments and suggestions. We have revised the manuscript accordingly. The attached are our item-by-item responses to the reviewers' comments and suggestions.
We believe that we have satisfactorily addressed the concerns of the reviewers and hope that the revised manuscript will now be suitable for publication in the Royal Society Open Science.